A 3-(alkylsulfonyl)pyridine-2-carboxylic acid is an important compound that serves as an intermediate in the production of pharmaceuticals and agrochemicals (e.g., WO 2013/018928), and various production methods are known.
Journal of Medicinal Chemistry, 1974, Vol. 17, No. 10, pp. 1065-1071, describes a method for producing 3-(methylthio)pyridine-2-carboxylic acid from 3-aminopicolinic acid, and Journal of Medicinal Chemistry, 1977, Vol. 20, No. 4, pp. 572-576, describes a method in which 3-(methylthio)pyridine-2-carboxylic acid is converted into a methyl ester, oxidized, and then hydrolyzed to produce 3-(methylsulfonyl)pyridine-2-carboxylic acid.
Meanwhile, for a method of producing a 3-(alkylthio)pyridine-2-carboxylic acid, a production method in which a 3-halogenopyridine-2-carboxylic acid is allowed to react with a thiol compound is known (WO 2013/018928).